This invention relates to spectrum analyzers in general and, more specifically, to a zero crossing based spectrum analyzer and method for determining the Discrete Fourier Transform (DFT) of a signal from the zero axis crossings of the signal rather than from its uniform (amplitude) samples.
Spectrum analyzers are employed in most of the modern signal processing systems for measuring the distribution of signal energy in frequency. Conventional digital spectrum analyzers consist of an anti-aliasing filter to band-limit the signal, an A/D converter to represent the analog signal by a sequence of numbers and a software based Fast Fourier transformer to compute the Discrete Fourier Transform. The conventional A/D converter method relies on multi-level quantization of samples taken at prescribed instants of time and requires a relatively high degree of hardware complexity. It is, accordingly, a general object of the invention to provide an improved apparatus and method for determining the DFT of a signal.
It is a specific object of the invention to provide a zero based spectrum analyzer for determining the DFT coefficients of the signal from the zero axis crossings of the signal rather than from its uniform (amplitude) samples.
It is another object of the invention to provide a spectrum analyzer that does not utilize an A/D converter.
It is a feature of the invention that signal sampling and quantization are eliminated.
It is another feature of the invention that since the A/D converter is avoided, the spectrum analyzer does not suffer from dynamic range problems and speed limitations.
It is a further feature of the invention that hardware complexity is reduced because the zero based spectrum analyzer and method of the present invention employs a zero crossing detector, a high-speed clock, a converter, control circuitry and a processor for converting the zero crossings into DFT coefficients.